"Michael A. Terrell" wrote in message
...


daestrom wrote:

You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.


I never said that at all, but I did say that the sped and phase have
to match to connect a new generator to a grid.


That isn't the case. A generator is brought on-line by carefully
regulating
the speed and getting it in phase. That is a bit tricky. But once tied
to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line.
The
speed set-point for the governor is run several hz up out of the way and
the
turbine controls are controlled by a 'load' setting. The operator dials
in
the amount of MW load they are supposed to carry, and the controls
monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.


If you would have read the entire thread, I described how the
generators are synched, and that the grid keeps them in sync unless
something goes wrong. I also stated that the generator was fed more
fuel or water to actually produce power for the grid rather than just
coasting along, in phase, one it was connected to the grid. I studied
the subject with college textbooks on power generation and distribution
when I was 13.
---------------



During grid disturbances, base load units will naturally speed
up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq
and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of
the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)


Of course the larger the spinning mass in the generator, the more the
inertia, and the less likely to be kicked out of phase. The
experimental nuclear power plant at Ft. Greely, Alaska was steam driven
and unable to adapt to rapid load changes so they blew out quite a few
bearings in the turbines before they finally gave up and shut it down.
---------

The problem is not the steam turbine/governor which responds relatively
quickly (much faster than a hydro machine), but likely in the reactor
dynamics and control. It appears that the machine was kicked off the system
and an uncontrolled shutdown occurred. Wiping of bearings can occur in
uncontrolled, coast slowly to a stop, shutdowns. It happened to "Big Ally"
in NYC in the '65 blackout.

Most college texts - at least in the past, when you were 13, didn't really
discuss synchronisation except for the general concept, nor the problem of
load sharing and the effects of governor "droop".

It is true that a heavier machine will respond more slowly for a given
accelerating power but this is a mixed blessing as it takes longer to bring
it under control and time is of the essence in considering system stability.
A smaller machine is more likely to swing rapidly but is normally easier
for the system to rein in (system impedances will affect this). I assume
that the experimental machine was fairly small as well as being weakly tied
to the system but there could well be other, control, problems with the
governor system and load sharing coordination.
--

Don Kelly @shawcross.ca
remove the X to answer
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